In cellular networks, there is always a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the cellular network is deployed.
In a cellular network where terminal devices (TDs) in a cell are served by network nodes there may be areas with high traffic, i.e. high concentration of TDs. By a TD is here meant a wireless user device, such as a user equipment (UE), mobile phone, etc. In such areas it is desirable to deploy additional capacity to ensure user satisfaction. The added capacity could be in the form of additional macro network nodes or network nodes with lower output power, such as micro network nodes or pico network nodes covering a particular area, thus concentrating the capacity boost to the particular area.
In the cellular network there may also be particular areas with coverage below a predetermined quality criterion where there thus may be a need for coverage extension. One way to mitigate this problem is to deploy a network node with low output power to concentrate the coverage boost to the particular areas. In general terms, a network node in the form of a so-called macro network node provides a wide area coverage (also called a macro cell). In the coverage area of the macro network node also low power network nodes could be deployed to provide small area capacity/coverage. Examples of such low power network nodes are so-called pico network nodes, relays and home network nodes (femto cells).
One argument for choosing network nodes with lower output power in the above scenarios is that the impact on the network as a whole may be minimized, e.g. for example concentrating any potential added interference of the network to the particular areas in which the additional network nodes with lower output power are deployed.
Additionally, there is currently a common drive in the direction towards the use of low power network nodes. The different terms used for these types of network deployments are Heterogeneous networks, multilayer networks or shortly HetNets. In such networks the underlay cells typically operate at lower reference (pilot/perch) signal powers compared to the macro cells. This means that if the cell selections as well as mobility decisions are based on received reference signal strengths, the downlink cell border is closer to the underlay network node than to the macro network node. If the uplink sensitivity for all cells is similar, or if the difference in uplink sensitivity is not equivalent to the difference in reference (pilot/perch) signal powers, then the uplink cell border will be different from the downlink cell border. This means that a TD served by the macro network node can have the best uplink to an underlay cell, causing extensive uplink interference even without having detected the underlay reference signal. Hence it may be difficult to provide a given service level in terms of e.g. throughput for the TD.
Hence, there is still a need for an improved radio resource usage determination in cellular networks.